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Tournassat Christophe - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic and Thermodynamic Insights into Anion Exchange by Green Rust
'American Chemical Society (ACS)', 2020Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougerite is a naturally occurring green rust, that is, a layered double hydroxide (LDH) containing iron (Fe). Fougerite was identified in natural settings such as Hydromorphic Soils. It is one of the few inorganic materials with large anion adsorption capacity that stems from the presence of isomorphic substitutions of Fe2+ by Fe3+ in its layers. The importance of anion adsorption in the interlayer of LDH has often been highlighted, but we are still missing a mechanistic understanding and a thermodynamic framework to predict the anion uptake by green rust. We combined laboratory and in operando synchrotron X-ray diffraction and scattering experiments with geochemical modeling to contribute to filling this gap. We showed that the overall exchange process in green rusts having nanometer and micrometer sizes can be seen as a simple anion exchange mechanism without dissolution–recrystallization or interstratification processes. A thermodynamic model of ion exchange, based on the Rothmund and Kornfeld convention, made it possible to predict the interlayer composition in a large range of conditions. This multiscale characterization can serve as a starting point for the building of robust and mechanistic geochemical models that will allow predicting the role of green rust on the geochemical cycle of ions, including nutrients, in Soils
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Échange anionique dans la Fougèrite : impact de la taille des cristaux et des des défauts structuraux
HAL CCSD, 2019Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougèrite is a Fe(II)/Fe(III) layered double hydroxide found in Hydromorphic Soils. Its layers are positively chargedbecause of the occurrence of mixed Fe2+/3+ valence states. The charge is compensated by exchangeable anions located in the interlayer space. Consequently, fougèrite, where present, participate to the biogeochemical cycling of anions, including nutrients or pollutants, in the environment. In this study, we carried out a detailed analysis of some of green rust (GR, synthetic fougèrite) ion exchange properties. We investigated the Cl-/SO42- exchange mechanism on two samples having similar layer structures, but different particle size: nanometric or micrometric size range particules. Samples were characterized by synchrotron high-energy Xray scattering and synchrotron in situ and time-resolved X-ray diffraction. Total anion exchange capacity and Cl-/SO42-selectivity coefficients (Kex) were obtained from modelling of aqueous chemistry data and microprobe analyses.The replacement of Cl- by SO42- followed a 2:1stoichiometry, and led to an increase of interlayer distances from 8.3 ± 0.1 Å to 11.3 ± 0.1 Å. No dissolution or recrystallization reactions were observed. An increase of SO42- occupancy in the interlayer led to an increase of therelative affinity of the exchanger for SO42- compared to Cl- Exchange data were adequately described with an anionexchange thermodynamic model using the Rothmund- Kornfeld convention. The model parameters were differentfor the nanometric GR particles and the micrometric GR particles, evincing a higher affinity of SO42- for the nanometric sample. This difference of affinity may originate from differences in layer stacking order in the two types of samples, the nanometric particles being turbostratic while the micrometric particles being 3D-ordered
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Échange anionique dans la Fougèrite : impact de la taille des cristaux et des des défauts structuraux
HAL CCSD, 2019Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougèrite, a Fe(II)/Fe(III) layered double hydroxide that was identified twenty years ago in Hydromorphic Soils, is a naturally-occurring form of green rust (GR). GR layers are positively charged because of the occurrence of mixed Fe2+/3+ valence states within the layers. The layer charge is compensated by anions in the interlayer space. These interlayer anions are exchangeable with anions present in the pore water. Where present, GR participate to the biogeochemical cycling of anions, including nutrients or pollutants, in the environment. In this study, we carried out a detailed analysis of green rust ion exchange properties, with the aim of contributing to a better understanding of the biogeochemical cycle of elements in Soils. In particular, we investigated the Cl-/SO42- exchange mechanism on two samples having similar layer structure, but particle size distributions either in the nanometer or in the micrometer size range. Samples were characterized by a combination of chemical and physical methods, including synchrotron high-energy X-Ray scattering and synchrotron in situ and time-resolved X-ray diffraction. The replacement of Cl- by SO42- followed a 2:1 stoichiometry, and led to an increase of interlayer distances, in agreement with an anion exchange mechanism without dissolution or recrystallization. Total anion exchange capacity and Cl-/SO42- selectivity coefficients (Kex) were inferred from modelling of aqueous chemistry data. Exchange data were adequately described by an anion exchange thermodynamic model using the Rothmund-Kornfeld convention with a Kex value of 0.58 and a β value of 3 for nanometric samples and 0.14 and a β value of 5 for micrometric samples
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Impact de la structure des rouilles vertes sur les processus d'échanges anioniques
HAL CCSD, 2018Co-Authors: Agnel Myriam, Grangeon Sylvain, Tournassat ChristopheAbstract:International audienceLayered materials such as clay minerals or oxides contribute significantly to soil reactivity because of their large specific surface area that promotes adsorption/desorption reactions.Among them, Foug`erite is a Fe(II)/Fe(III) layered double hydroxide that was identified twentyyears ago in Hydromorphic Soils. Foug`erite has a layer structure resembling that of the so-calledGreen Rust (GR) whose color is due to the mixed Fe valence in their structure. GR layers arepositively charged because of the presence isomorphic substitutions (e.g. Fe3+ in place of Fe2+)and possibly vacancies. Layer charge compensation at the mineral scale is ensured by anionslocated in the interlayer space. These interlayer anions can be exchanged with anions present insurrounding pore water. Consequently, GR participate to the biogeochemical cycling of anionsin the environment, including nutrients or pollutants. In this study, we carried out a detailedanalysis of green rust structure in order to better quantify these biogeochemical cyclings. Inparticular, we performed laboratory and synchrotron experiments that allowed deciphering themechanisms of chloride for sulphate exchange. The effect of particle size was investigated usingtwo types of samples, one being nanometric and the other one micrometric, that we synthesizedand characterized. It could be demonstrated that sulphate replaces chloride in the interlayerspace. These experiments shed light on the relationship between structure and reactivity ofthese phases
Agnel Myriam - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic and Thermodynamic Insights into Anion Exchange by Green Rust
'American Chemical Society (ACS)', 2020Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougerite is a naturally occurring green rust, that is, a layered double hydroxide (LDH) containing iron (Fe). Fougerite was identified in natural settings such as Hydromorphic Soils. It is one of the few inorganic materials with large anion adsorption capacity that stems from the presence of isomorphic substitutions of Fe2+ by Fe3+ in its layers. The importance of anion adsorption in the interlayer of LDH has often been highlighted, but we are still missing a mechanistic understanding and a thermodynamic framework to predict the anion uptake by green rust. We combined laboratory and in operando synchrotron X-ray diffraction and scattering experiments with geochemical modeling to contribute to filling this gap. We showed that the overall exchange process in green rusts having nanometer and micrometer sizes can be seen as a simple anion exchange mechanism without dissolution–recrystallization or interstratification processes. A thermodynamic model of ion exchange, based on the Rothmund and Kornfeld convention, made it possible to predict the interlayer composition in a large range of conditions. This multiscale characterization can serve as a starting point for the building of robust and mechanistic geochemical models that will allow predicting the role of green rust on the geochemical cycle of ions, including nutrients, in Soils
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Échange anionique dans la Fougèrite : impact de la taille des cristaux et des des défauts structuraux
HAL CCSD, 2019Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougèrite is a Fe(II)/Fe(III) layered double hydroxide found in Hydromorphic Soils. Its layers are positively chargedbecause of the occurrence of mixed Fe2+/3+ valence states. The charge is compensated by exchangeable anions located in the interlayer space. Consequently, fougèrite, where present, participate to the biogeochemical cycling of anions, including nutrients or pollutants, in the environment. In this study, we carried out a detailed analysis of some of green rust (GR, synthetic fougèrite) ion exchange properties. We investigated the Cl-/SO42- exchange mechanism on two samples having similar layer structures, but different particle size: nanometric or micrometric size range particules. Samples were characterized by synchrotron high-energy Xray scattering and synchrotron in situ and time-resolved X-ray diffraction. Total anion exchange capacity and Cl-/SO42-selectivity coefficients (Kex) were obtained from modelling of aqueous chemistry data and microprobe analyses.The replacement of Cl- by SO42- followed a 2:1stoichiometry, and led to an increase of interlayer distances from 8.3 ± 0.1 Å to 11.3 ± 0.1 Å. No dissolution or recrystallization reactions were observed. An increase of SO42- occupancy in the interlayer led to an increase of therelative affinity of the exchanger for SO42- compared to Cl- Exchange data were adequately described with an anionexchange thermodynamic model using the Rothmund- Kornfeld convention. The model parameters were differentfor the nanometric GR particles and the micrometric GR particles, evincing a higher affinity of SO42- for the nanometric sample. This difference of affinity may originate from differences in layer stacking order in the two types of samples, the nanometric particles being turbostratic while the micrometric particles being 3D-ordered
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Échange anionique dans la Fougèrite : impact de la taille des cristaux et des des défauts structuraux
HAL CCSD, 2019Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougèrite, a Fe(II)/Fe(III) layered double hydroxide that was identified twenty years ago in Hydromorphic Soils, is a naturally-occurring form of green rust (GR). GR layers are positively charged because of the occurrence of mixed Fe2+/3+ valence states within the layers. The layer charge is compensated by anions in the interlayer space. These interlayer anions are exchangeable with anions present in the pore water. Where present, GR participate to the biogeochemical cycling of anions, including nutrients or pollutants, in the environment. In this study, we carried out a detailed analysis of green rust ion exchange properties, with the aim of contributing to a better understanding of the biogeochemical cycle of elements in Soils. In particular, we investigated the Cl-/SO42- exchange mechanism on two samples having similar layer structure, but particle size distributions either in the nanometer or in the micrometer size range. Samples were characterized by a combination of chemical and physical methods, including synchrotron high-energy X-Ray scattering and synchrotron in situ and time-resolved X-ray diffraction. The replacement of Cl- by SO42- followed a 2:1 stoichiometry, and led to an increase of interlayer distances, in agreement with an anion exchange mechanism without dissolution or recrystallization. Total anion exchange capacity and Cl-/SO42- selectivity coefficients (Kex) were inferred from modelling of aqueous chemistry data. Exchange data were adequately described by an anion exchange thermodynamic model using the Rothmund-Kornfeld convention with a Kex value of 0.58 and a β value of 3 for nanometric samples and 0.14 and a β value of 5 for micrometric samples
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Impact de la structure des rouilles vertes sur les processus d'échanges anioniques
HAL CCSD, 2018Co-Authors: Agnel Myriam, Grangeon Sylvain, Tournassat ChristopheAbstract:International audienceLayered materials such as clay minerals or oxides contribute significantly to soil reactivity because of their large specific surface area that promotes adsorption/desorption reactions.Among them, Foug`erite is a Fe(II)/Fe(III) layered double hydroxide that was identified twentyyears ago in Hydromorphic Soils. Foug`erite has a layer structure resembling that of the so-calledGreen Rust (GR) whose color is due to the mixed Fe valence in their structure. GR layers arepositively charged because of the presence isomorphic substitutions (e.g. Fe3+ in place of Fe2+)and possibly vacancies. Layer charge compensation at the mineral scale is ensured by anionslocated in the interlayer space. These interlayer anions can be exchanged with anions present insurrounding pore water. Consequently, GR participate to the biogeochemical cycling of anionsin the environment, including nutrients or pollutants. In this study, we carried out a detailedanalysis of green rust structure in order to better quantify these biogeochemical cyclings. Inparticular, we performed laboratory and synchrotron experiments that allowed deciphering themechanisms of chloride for sulphate exchange. The effect of particle size was investigated usingtwo types of samples, one being nanometric and the other one micrometric, that we synthesizedand characterized. It could be demonstrated that sulphate replaces chloride in the interlayerspace. These experiments shed light on the relationship between structure and reactivity ofthese phases
Alain Tabbagh - One of the best experts on this subject based on the ideXlab platform.
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quantifying multiple electromagnetic properties in emi surveys a case study of Hydromorphic Soils in a volcanic context the lac du puy france
Geoderma, 2020Co-Authors: Francoisxavier Simon, Mathias Pareilhpeyrou, Solene Buvat, Alfredo Mayoral, Philippe Labazuy, Karim Kelfoun, Alain TabbaghAbstract:We used two different loop-loop electromagnetic induction (EMI) devices to determine the 3D geometry and morphology of the pedo-sedimentary filling and underlying basaltic bedrock of a former wetland in a volcanic soil area, the Lac du Puy depression (Auvergne, France). Electrical conductivity (or resistivity) is usually sufficient for environmental and soil science applications, but the local volcanic context of the survey area results in high values of magnetic susceptibility and possible electrical polarization effects. Therefore we investigated the roles of the four properties: electrical conductivity, magnetic susceptibility, magnetic viscosity and dielectric permittivity. We created models using these four properties for the two coil configurations of each device in order to assess the degree to which each of the properties contributed to the recorded electromagnetic signal. The results show that electrical conductivity controls the quadrature component of the secondary field response but that it can be affected by high values of magnetic viscosity, while magnetic susceptibility controls the in-phase component. Moreover, the low frequencies imply a limited contribution of dielectric permittivity to the in-phase component, except in the cases of higher permittivity or frequency values or greater inter-coil separation. Based on these observations, we propose a way to map the apparent properties from field measurements. We then carried out a 1D inversion, first by considering the electrical conductivity alone and secondly by taking all the electromagnetic properties into account. The results show that there is a marked contrast in the complex magnetic susceptibility between the sedimentary in-fill and the border of the Lac de Puy depression, (stronger than for the electrical conductivity), and that permittivity is unlikely to have a significant influence. The shape and nature of the sedimentary in-fill was thus considerably refined by the second inversion results based on the three other properties. These data, combined with litho-stratigraphic observations from a previous study, allowed the lateral continuity and geometry of the in-fill to be assessed across the whole basin. Results are also consistent with previous interpretations of the depression as a pseudo-sinkhole, a relatively common morphology in volcanic plateaus. Analysis of the magnetic properties also made it possible to characterize the spatial variation of some key features related to Hydromorphic processes, such as clayey granularity and the development of iron oxides/hydroxides. This opens up the possibility for using new methods for rapid spatial and pedological characterization of Hydromorphic Soils and palaeoSoils.
Grangeon Sylvain - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic and Thermodynamic Insights into Anion Exchange by Green Rust
'American Chemical Society (ACS)', 2020Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougerite is a naturally occurring green rust, that is, a layered double hydroxide (LDH) containing iron (Fe). Fougerite was identified in natural settings such as Hydromorphic Soils. It is one of the few inorganic materials with large anion adsorption capacity that stems from the presence of isomorphic substitutions of Fe2+ by Fe3+ in its layers. The importance of anion adsorption in the interlayer of LDH has often been highlighted, but we are still missing a mechanistic understanding and a thermodynamic framework to predict the anion uptake by green rust. We combined laboratory and in operando synchrotron X-ray diffraction and scattering experiments with geochemical modeling to contribute to filling this gap. We showed that the overall exchange process in green rusts having nanometer and micrometer sizes can be seen as a simple anion exchange mechanism without dissolution–recrystallization or interstratification processes. A thermodynamic model of ion exchange, based on the Rothmund and Kornfeld convention, made it possible to predict the interlayer composition in a large range of conditions. This multiscale characterization can serve as a starting point for the building of robust and mechanistic geochemical models that will allow predicting the role of green rust on the geochemical cycle of ions, including nutrients, in Soils
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Échange anionique dans la Fougèrite : impact de la taille des cristaux et des des défauts structuraux
HAL CCSD, 2019Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougèrite is a Fe(II)/Fe(III) layered double hydroxide found in Hydromorphic Soils. Its layers are positively chargedbecause of the occurrence of mixed Fe2+/3+ valence states. The charge is compensated by exchangeable anions located in the interlayer space. Consequently, fougèrite, where present, participate to the biogeochemical cycling of anions, including nutrients or pollutants, in the environment. In this study, we carried out a detailed analysis of some of green rust (GR, synthetic fougèrite) ion exchange properties. We investigated the Cl-/SO42- exchange mechanism on two samples having similar layer structures, but different particle size: nanometric or micrometric size range particules. Samples were characterized by synchrotron high-energy Xray scattering and synchrotron in situ and time-resolved X-ray diffraction. Total anion exchange capacity and Cl-/SO42-selectivity coefficients (Kex) were obtained from modelling of aqueous chemistry data and microprobe analyses.The replacement of Cl- by SO42- followed a 2:1stoichiometry, and led to an increase of interlayer distances from 8.3 ± 0.1 Å to 11.3 ± 0.1 Å. No dissolution or recrystallization reactions were observed. An increase of SO42- occupancy in the interlayer led to an increase of therelative affinity of the exchanger for SO42- compared to Cl- Exchange data were adequately described with an anionexchange thermodynamic model using the Rothmund- Kornfeld convention. The model parameters were differentfor the nanometric GR particles and the micrometric GR particles, evincing a higher affinity of SO42- for the nanometric sample. This difference of affinity may originate from differences in layer stacking order in the two types of samples, the nanometric particles being turbostratic while the micrometric particles being 3D-ordered
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Échange anionique dans la Fougèrite : impact de la taille des cristaux et des des défauts structuraux
HAL CCSD, 2019Co-Authors: Agnel Myriam, Grangeon Sylvain, Fauth François, Elkaim Erik, Claret Francis, Roulet Marjorie, Warmont Fabienne, Tournassat ChristopheAbstract:International audienceFougèrite, a Fe(II)/Fe(III) layered double hydroxide that was identified twenty years ago in Hydromorphic Soils, is a naturally-occurring form of green rust (GR). GR layers are positively charged because of the occurrence of mixed Fe2+/3+ valence states within the layers. The layer charge is compensated by anions in the interlayer space. These interlayer anions are exchangeable with anions present in the pore water. Where present, GR participate to the biogeochemical cycling of anions, including nutrients or pollutants, in the environment. In this study, we carried out a detailed analysis of green rust ion exchange properties, with the aim of contributing to a better understanding of the biogeochemical cycle of elements in Soils. In particular, we investigated the Cl-/SO42- exchange mechanism on two samples having similar layer structure, but particle size distributions either in the nanometer or in the micrometer size range. Samples were characterized by a combination of chemical and physical methods, including synchrotron high-energy X-Ray scattering and synchrotron in situ and time-resolved X-ray diffraction. The replacement of Cl- by SO42- followed a 2:1 stoichiometry, and led to an increase of interlayer distances, in agreement with an anion exchange mechanism without dissolution or recrystallization. Total anion exchange capacity and Cl-/SO42- selectivity coefficients (Kex) were inferred from modelling of aqueous chemistry data. Exchange data were adequately described by an anion exchange thermodynamic model using the Rothmund-Kornfeld convention with a Kex value of 0.58 and a β value of 3 for nanometric samples and 0.14 and a β value of 5 for micrometric samples
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Impact de la structure des rouilles vertes sur les processus d'échanges anioniques
HAL CCSD, 2018Co-Authors: Agnel Myriam, Grangeon Sylvain, Tournassat ChristopheAbstract:International audienceLayered materials such as clay minerals or oxides contribute significantly to soil reactivity because of their large specific surface area that promotes adsorption/desorption reactions.Among them, Foug`erite is a Fe(II)/Fe(III) layered double hydroxide that was identified twentyyears ago in Hydromorphic Soils. Foug`erite has a layer structure resembling that of the so-calledGreen Rust (GR) whose color is due to the mixed Fe valence in their structure. GR layers arepositively charged because of the presence isomorphic substitutions (e.g. Fe3+ in place of Fe2+)and possibly vacancies. Layer charge compensation at the mineral scale is ensured by anionslocated in the interlayer space. These interlayer anions can be exchanged with anions present insurrounding pore water. Consequently, GR participate to the biogeochemical cycling of anionsin the environment, including nutrients or pollutants. In this study, we carried out a detailedanalysis of green rust structure in order to better quantify these biogeochemical cyclings. Inparticular, we performed laboratory and synchrotron experiments that allowed deciphering themechanisms of chloride for sulphate exchange. The effect of particle size was investigated usingtwo types of samples, one being nanometric and the other one micrometric, that we synthesizedand characterized. It could be demonstrated that sulphate replaces chloride in the interlayerspace. These experiments shed light on the relationship between structure and reactivity ofthese phases
J M R Genin - One of the best experts on this subject based on the ideXlab platform.
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oxidation modes and thermodynamics of feii iii oxyhydroxycarbonate green rust dissolution precipitation versus in situ deprotonation
Geochimica et Cosmochimica Acta, 2010Co-Authors: Christian Ruby, Mustapha Abdelmoula, Guillaume Morin, Georges Onanguema, Sebastien Naille, Aurelien Renard, Varsha Khare, J M R GeninAbstract:Abstract Fe II–III hydroxycarbonate green rust GR(CO 3 2− ), Fe II 4 Fe III 2 (OH) 12 CO 3 ·3H 2 O, is oxidized in aqueous solutions with varying reaction kinetics. Rapid oxidation with either H 2 O 2 or dissolved oxygen under neutral and alkaline conditions leads to the formation of ferric oxyhydroxycarbonate GR(CO 3 2− )∗, Fe III 6 O 12 H 8 CO 3 ·3H 2 O, via a solid-state reaction. By decreasing the flow of oxygen bubbled in the solution, goethite α-FeOOH forms by dissolution–precipitation mechanism whereas a mixture of non-stoichiometric magnetite Fe (3− x ) O 4 and goethite is observed for lower oxidation rates. The intermediate Fe II–III oxyhydroxycarbonate of formula Fe II 6(1− x ) Fe III 6 x O 12 H 2(7−3 x ) CO 3 ·3H 2 O, i.e. GR( x )∗ for which x ϵ [1/3, 1], is the synthetic compound that is homologous to the fougerite mineral present in Hydromorphic gleysol; in situ oxidation accounts for the variation of ferric molar fraction x = [Fe III ]/{[Fe II ]+[Fe III ]} observed in the field as a function of depth and season but limited to the range [1/3, 2/3]. The domain of stability for partially oxidized green rust is observed in the E h -pH Pourbaix diagrams if thermodynamic properties of GR( x )∗ is compared with those of lepidocrocite, γ-FeOOH, and goethite, α-FeOOH. Electrochemical equilibrium between GR( x )∗ and Fe II in solution corresponds to E h -pH conditions close to those measured in the field. Therefore, the reductive dissolution of GR( x )∗ can explain the relatively large concentration of Fe II measured in aqueous medium of Hydromorphic Soils containing fougerite.
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thermodynamic equilibria in aqueous suspensions of synthetic and natural fe ii fe iii green rusts occurrences of the mineral in Hydromorphic Soils
Environmental Science & Technology, 1998Co-Authors: J M R Genin, Guilhem Bourrie, Fabienne Trolard, Mustapha Abdelmoula, Anne Jaffrezic, Philippe Refait, Veronique Maitre, Bernard Humbert, A HerbillonAbstract:Synthetic green rusts, GRs, are prepared by oxidation of Fe(OH)2 incorporating Cl-, SO42-, or CO32- ions. Eh−pH diagrams are drawn, and thermodynamic data are derived. A GR incorporating OH- ions, GR1(OH-), is suspected to exist like similar other M(II)−M(III) compounds. GRs form as corrosion products of steels, implying microbially induced corrosion. Mossbauer and Raman spectroscopies allowed the identification of GR in samples extracted from Hydromorphic Soils scattered over Brittany, France. This mineral has a varying Fe(III)/Fe(II) ratio. At Fougeres, it increases with depth till the oc currence of more oxidized ferric oxyhydroxide. In the same sites, soil solutions are collected and prevented from any oxidation and photoreduction. In large ranges of pH, pe, and Fe(II) concentration variations, soil solutions are in equilibrium with a Fe(II)−Fe(III) compound, a GR1 mineral with pyroaurite-like structure incorporating OH- ions and having the formula [FeII(1-x)FeIIIx(OH)2]+x·[xOH]-x ≡ Fe(OH)(2+x). Compu...
